1. Field of the Invention
This invention relates to a harrowing device for harrowing topsoil of a race track field for horse racing, agricultural land or the like.
2. Description of the Prior Art
Conventionally, harrowing devices have been used for crushing and leveling the topsoil of a race track field for horse racing before starting the race in order to facilitate the racing of horses on the track and to maintain the beauty of the race track.
The conventional harrowing devices are generally provided with a frame, a plurality of blade holders and blades and a hauling member. In the harrowing devices with this configuration, when the devices are hauled on the field using the hauling member, the blades harrow and crush the topsoil of the field to level the ground.
In this harrowing operation, the front edges of the blades are inclined to wear away more than the rear edges of the blades. When the front edge wears away, the efficient of the harrowing operation is reduced. Therefore, to equalize the rate of abrasion of the front edge and the rear edge, when the abrasion advances a little, the blade is reversed so that the front edge and the rear edge are used alternately.
In the turning operation, first a plurality of bolts and nuts which mount the blade to the blade holder are loosened, and then the blades are removed from the blade holders. After that, the blade is reversed so that the front edge becomes the rear edge of the blades, and then the blades are remounted on the blade holders and the bolts and the nuts are tightened.
However, because there are many blades, bolts and nuts, this turning operation is very troublesome. Further, in the case where the cross section of the blade holder has a rhombic shape or a shape of opposing wedges, and the cross section of the shank of the blade for inserting into the blade holder has a rhombic shape or a shape of opposing wedges, the blade cannot be easily removed from the blade holder.
Moreover, in the conventional harrowing devices of the type using bolts and nuts, the bolts and the nuts can become loose, so that the blade will frequently fall away from the blade holder during the harrowing operation. In addition, the blade cannot be easily removed because of rusting of the bolts and the nuts.